新增：管理后台前端页面，以及openspec内容。

openspec/changes/fix-frontend-issues/proposal.md

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+# Change: Fix Frontend Issues and Add Best Practices
+
+## Why
+The frontend project has some issues that need to be fixed, including:
+1. Sass @import rules deprecation warnings (will be removed in Dart Sass 3.0.0)
+2. Theme store initialization order error causing `ReferenceError: Cannot access 'themeStore' before initialization`
+
+This change aims to fix these issues and establish best practices to avoid similar problems in future frontend development.
+
+## What Changes
+- Fix theme store initialization order by initializing Pinia first before using stores
+- Replace Sass @import rules with @use rules to eliminate deprecation warnings
+- Add best practices documentation for frontend development
+
+## Impact
+- Affected specs: frontend-integration
+- Affected code: admin-web/src/main.js, admin-web/src/styles/main.scss
+- Dependencies: None